EP722850B1 disclosed a low-permeability thermoplastic elastomer composition that is superior as a gas-barrier layer in pneumatic tires. This thermoplastic composition comprises a low-permeability thermoplastic matrix such as polyamides or blends of polyamides, in which a low-permeability rubber such as brominated poly(isobutylene-co-p-methylstyrene) (i.e., or BIMS) is dispersed. Subsequently, in both EP857761A1 and EP969039A1, viscosity ratio between the thermoplastic matrix and the rubber dispersion was specified in order to achieve phase continuity in thermoplastic and fine rubber dispersions. Criticality of smaller rubber dispersions was recognized in EP969039A1 in these thermoplastic elastomers for delivering acceptable durability especially for their usage as innerliners in pneumatic tires.
Further improvement in impermeability of these low-permeability thermoplastic elastomers could be achieved by imposing planar orientation. In WO 0214410, introduction of orientation into a thermoplastic elastomer film for property enhancement and for permeability reduction was disclosed conceptually. No experimental data were provided in this patent application. Further, the process specified in this application involves bi-axial orientation of cast film through drafting, tentering, and heatsetting by assuming the film in discussion has the strain hardening characteristics and suitable stretching dynamics. In the present invention, the planar orientation in a thermoplastic elastomer cast film is imposed simply by the film casting and/or film blowing process and film blowing for the improvement in film properties. This thermoplastic elastomer film does not have the suitable stretching dynamics for it to be oriented by a sequential bi-axial orientation process.